1. Field of the Invention
This invention relates to optical pulse generators and to passive devices therefor. Accordingly, it is a general object of this invention to provide new and improved apparatus of such character.
2. Description of the Prior Art
Devices that produce trains of short pulses (pulse-width .tau..sub.p .ltorsim.10 ps) are useful in optical communications and in many areas of basic physics research. One widely used method of obtaining such pulses is the technique of modelocking in which a property of a laser source (e.g. gain, loss, frequency or injection current) is modulated within the laser cavity itself to produce pulses as short as 0.1 ps. However, not all lasers can be effectively modelocked. Thus, there is a need for passive devices, external to and separate from the laser cavity, which can produce short pulses when excited by a laser of sufficient power.
A known passive pulse generator includes a Fabry-Perot cavity filled with a medium whose refractive index depends on the light intensity. The light-induced changes in refractive index are attributed to two basic mechanisms, one of which is thermal in origin, limiting the speed of the device to the microsecond regime. A Fabry-Perot cavity, however, is not a waveguide structure; it is a bulk structure in which feedback occurs at the end of the medium by means of mirrored reflection. Disadvantageously, it cannot be easily combined with other optical components on one substrate to create an integrated optical circuit.